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“The moon’s actual distance from the earth was the first thing to be attended to. Now, the mean or average interval between the centres of the two planets is 59.9643 of the earth’s equatorial radii, or only about 237,000 miles. I say the mean or average interval. But it must be borne in mind that the form of the moon’s orbit being an ellipse of eccentricity amounting to no less than 0.05484 of the major semi-axis of the ellipse itself, and the earth’s centre being situated in its focus, if I could, in any manner, contrive to meet the moon, as it were, in its perigee, the above mentioned distance would be materially diminished. But, to say nothing at present of this possibility, it was very certain that, at all events, from the 237,000 miles I would have to deduct the radius of the earth, say 4,000, and the radius of the moon, say 1080, in all 5,080, leaving an actual interval to be traversed, under average circumstances, of 231,920 miles. Now this, I reflected, was no very extraordinary distance. Travelling on land has been repeatedly accomplished at the rate of thirty miles per hour, and indeed a much greater speed may be anticipated. But even at this velocity, it would take me no more than 322 days to reach the surface of the moon. There were, however, many particulars inducing me to believe that my average rate of travelling might possibly very much exceed that of thirty miles per hour, and, as these considerations did not fail to make a deep impression upon my mind, I will mention them more fully hereafter.

“The next point to be regarded was a matter of far greater importance. From indications afforded by the barometer, we find that, in ascensions from the surface of the earth we have, at the height of 1,000 feet, left below us about one-thirtieth of the entire mass of atmospheric air, that at 10,600 we have ascended through nearly one-third; and that at 18,000, which is not far from the elevation of Cotopaxi, we have surmounted one-half the material, or, at all events, one-half the ponderable, body of air incumbent upon our globe. It is also calculated that at an altitude not exceeding the hundredth part of the earth’s diameter — that is, not exceeding eighty miles — the rarefaction would be so excessive that animal life could in no manner be sustained, and, moreover, that the most delicate means we possess of ascertaining the presence of the atmosphere would be inadequate to assure us of its existence. But I did not fail to perceive that these latter calculations are founded altogether on our experimental knowledge of the properties of air, and the mechanical laws regulating its dilation and compression, in what may be called, comparatively speaking, the immediate vicinity of the earth itself; and, at the same time, it is taken for granted that animal life is and must be essentially incapable of modification at any given unattainable distance from the surface. Now, all such reasoning and from such data must, of course, be simply analogical. The greatest height ever reached by man was that of 25,000 feet, attained in the aeronautic expedition of Messieurs Gay-Lussac and Biot. This is a moderate altitude, even when compared with the eighty miles in question; and I could not help thinking that the subject admitted room for doubt and great latitude for speculation.

“But, in point of fact, an ascension being made to any given altitude, the ponderable quantity of air surmounted in any farther ascension is by no means in proportion to the additional height ascended (as may be plainly seen from what has been stated before), but in a ratio constantly decreasing. It is therefore evident that, ascend as high as we may, we cannot, literally speaking, arrive at a limit beyond which no atmosphere is to be found. It must exist, I argued; although it may exist in a state of infinite rarefaction.